稻草覆盖对红壤旱坡地水力性质及水分状况的影响

Effects of straw mulch on soil hydraulic properties and water status in sloping red soil farmlands

为探明红壤旱坡地应用稻草覆盖的雨季和旱季保水作用,在湖北省咸宁市第四纪红色黏土母质发育的红壤8°坡地上开展田间试验,以不覆盖为对照,研究稻草覆盖对红壤的持水性、水分有效性、供水性、导水性、含水量及储水量的影响。结果表明:稻草覆盖改善了土壤的持水性和水分有效性,覆盖当年土壤田间持水量、凋萎系数和有效水容量分别比对照提高6.0%、7.3%和4.4%;稻草覆盖显著减缓了雨季红壤表层饱和导水率的下降幅度,尤其是大雨期间保护地表饱和导水性的作用更明显,102.8 mm的降雨结束之后,稻草覆盖的土壤平均饱和导水率是对照的2.7倍;稻草覆盖对土壤的供水性及非饱和导水性的影响表现为低吸力段增强,高吸力段减弱;土壤储水量在集中降雨阶段的上升幅度和在降雨间歇期的下降幅度都表现为稻草覆盖<对照。总体上,土壤储水量均表现为稻草覆盖>对照;稻草覆盖增加雨季土壤储水量主要通过增加入渗,而增加旱季土壤储水量主要通过减少蒸散发;稻草覆盖增加雨季土壤储水量的作用有限,且保水作用雨季<旱季。因此,稻草覆盖在红壤旱坡地上的雨季和旱季的保水途径、特点及作用大小都不同。

Although straw mulch is widely used to improve soil water and heat in farmlands, the comprehensive effects of application of straw mulch depend on environmental conditions such as soil and climate. In subtropical China, productivity of sloping red soil farmlands is limited by severe rain-induced erosion in the wet spring-summer period and frequent seasonal droughts in the dry summer-autumn period. There were possible hydrological connections between soil erosion and drought. At present, it has remained unclear how temporal variations in soil hydraulic properties due to local soil and water loss affect soil water storage in wet and dry seasons. In addition, little attention has been paid to comparison of the different effects of straw mulch on soil water storage in the two seasons. However, related knowledge is important to increase water use in local fields. The objectives of this study were to explore the role of straw mulch on preserving soil water in the wet and dry seasons in sloping red soil farmlands. To this end, a field experiment was performed in Xianning City of Hubei Province with red soils（Ultisols） originating from Quaternary red clays. In an experimental field of low hill with 8° slope, two treatments, including rice straw mulch over surface soil（SW） and no mulch（CK, control）, were used to analyze the effects of straw mulch on variations in soil water retention, water availability, water supply, hydraulic conductivity, water content and water storage. Results showed that SW improved soil water retention and water availability, with increases in field water capacity, wilting coefficient and available water holding capacity of respectively 6.0%, 7.3% and 4.4% over CK. SW also greatly lowered the decline in saturated hydraulic conductivity of the surface layer of the red soil, especially under intense rainfall events. After 102.8 mm of rainfall event, mean soil saturated hydraulic conductivity under SW was on average 2.7 times that under CK. After straw mulch, water supply and unsaturated hydraulic conductivity of the soil increased when soil water suction was low, and decreased as soil water suction was high. Compared with CK, SW had a smaller rise in soil water storage in high-intensity precipitation events and less decline in soil water storage during no rain periods. In general, there was more soil water storage under SW than CK. Straw mulch increased soil water storage in wet and dry seasons respectively by increasing field infiltration and reducing evapotranspiration. Under SW, soil water storage increased only in limited volume in the rainy season and water preservation capability was less than that in the dry season. It was concluded that the ways, features and capabilities of soil water preservation by straw mulch were different for the wet season and dry season in sloping red soil farmlands in subtropical China.